I have Cisco FTD installed which is routing traffic between two subnets on "inside" interface. When we are copying files between these two subnets through SMB2 protocol, I can see that it's going very slow. When I did a capture, I came to know that there were a lot of TCP Retransmissions in my packet capture. I have configured a Pre-Filter Policy, Trust the traffic in ACP and TCP Bypass but nothing is improving the situation.
I was wondering if someone can have tips on how to tweak or have a logical explanation to this behavior.
Any help or suggestion will be highly appreciated.
Give some metrics. 'Slow' and 'a lot of' is not data. What is the throughput in bit/s ? Watch I/O graphs in Wireshark. What is the ratio of retransmitted packets to all TCP packets? How many retransmissions per second?